semihosting: permit redirection of semihosting I/O to TCP

This command permits the usage of a TCP port to perform debug and stdio
operations:
 - debug : READC, WRITEC and WRITE0
 - stdio : READ, WRITE

This will permit the separation of semihosting message from OpenOCD log,
and separate semihosting messages per core.

syntax: arm semihosting_redirect (disable | tcp <port> [debug|stdio|all])

this allows to select which operations to be performed via TCP (debug,
stdio or all (default)).

Note: for stdio operations, only I/O from/to ':tt' file descriptors are
redirected.

tested using netcat on ubuntu

Change-Id: I37053463667ba109d52429d4f98bc98d0ede298d
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/5562
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

src/target/semihosting_common.h

@@ -26,6 +26,7 @@
 #include <stdbool.h>
 #include <time.h>
 #include "helper/replacements.h"
+#include <server/server.h>
 
 /*
  * According to:
@@ -95,6 +96,13 @@ enum semihosting_reported_exceptions {
 	ADP_STOPPED_RUN_TIME_ERROR = ((2 << 16) + 35),
 };
 
+enum semihosting_redirect_config {
+	SEMIHOSTING_REDIRECT_CFG_NONE,
+	SEMIHOSTING_REDIRECT_CFG_DEBUG,
+	SEMIHOSTING_REDIRECT_CFG_STDIO,
+	SEMIHOSTING_REDIRECT_CFG_ALL,
+};
+
 struct target;
 
 /*
@@ -105,6 +113,15 @@ struct semihosting {
 	/** A flag reporting whether semihosting is active. */
 	bool is_active;
 
+	/** Semihosting STDIO file descriptors */
+	int stdin_fd, stdout_fd, stderr_fd;
+
+	/** redirection configuration, NONE by default */
+	enum semihosting_redirect_config redirect_cfg;
+
+	/** Handle to redirect semihosting print via tcp */
+	struct connection *tcp_connection;
+
 	/** A flag reporting whether semihosting fileio is active. */
 	bool is_fileio;